Biomass hydrolysis

Abstract

High-yielding method for chemical hydrolysis of lignocellulose into monosaccharides. The process of the invention can additionally be applied to cellulose, xylan and related biomass polysaccharides, such as galactan, mannan, or arabinan. The method is employed for hydrolysis of a biomass polysaccharide substrate. The process is carried out in an ionic liquid in which cellulose is soluble in the presence of catalytic acid at a temperature sufficiently high to initiate hydrolysis. Water is added to the reaction mixture after initiation of hydrolysis at a rate controlled to avoid precipitation yet avoid undesired sugar dehydration products such ad HMF. Hydrolysis product is useful as feedstock for fermentations including fermentation processes for ethanol, butanol and other fuels.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. provisional application 61 / 222,397, filed Jul. 1, 2009 which application is incorporated by reference in its entirety herein.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]This invention was made with United States government support awarded by the following agencies: DOE DE-FC02-07ER64494. The United States government has certain rights in this invention.BACKGROUND OF THE INVENTION[0003]Abundant plant biomass could become a sustainable source of fuels and chemicals. Unlocking this potential requires the economical conversion of recalcitrant lignocellulose into useful intermediates, such as sugars. We report a high-yielding process for the chemical hydrolysis of lignocellulose into monosaccharides. Adding water gradually to a chloride ionic liquid containing catalytic acid leads to a nearly 90% yield of glucose from cellulose and 70-80% yield of sugars from untreated corn s...

AI Technical Summary

Benefits of technology

[0022]In the case of cellulose or other polysaccharide, hydrolysis is continued to achieve a maximum yield of glucose, while minimizing the production of undesired monosaccharide dehydration by-products, such as hydroxymethylfuran (HMF). In specific embodiments, the glucose yield from cellulose hydrolysis is equal to or greater than 50%. In specific embodiments, the glucose yield from cellulose hydrolysis is equal to or greater than 75%. In specific embodiments, the glucose yield from cellulose hydrolysis is equal to or greater than 85%. In specific embodiments, the hydrolysis reaction is carried out for 1-10 hours, more preferably 1-5 hours, and more specifically 2-3 hours. In a specific embodiment, the reaction is carried out at a temperature ranging from 100-110° C. for 1-4 hours and more specifically for 2-3 hours. The addition of water as described decreases the formation of undesired by-products of cellulose hydrolysis, specifically hydroxymethylfuran (HMF), which are believed at least in part to result from monosaccharide dehydration. In specific embodiments, the yield of HMF in the hydrolysis is 10% or less. In specific embodiments, the yield of HMF in the hydrolysis is 5% or less. The monosaccharide products of hydrolysis can be separated from ionic liquid and employed as a source of monosaccharide for any desired application. In a specific embodiment, the products of hydrolysis can be separated from ionic liquid and employed as a source of monosaccharide for growth of microorganisms and the production of fermentation products, such as ethanol. In an embodiment, the ionic liquid can be separated from the hydrolysis product, particularly by passage through an appropriate ion exchange column and the ionic liquid can optionally be recycled for reuse.

[0029]In the processes herein, water is added after acid catalyzed hydrolysis of cellulose is initiated to enhance glucose yields and minimize by-product generation, e.g., generation of HMF. The timing and amount of water addition is controlled to avoid cellulose precipitation, increase glucose yield (or yield of glucose combined with other monosaccharide) and minimize undesired dehydration by-product, e.g., HMF, formation. It will be readily appreciated that the initial reaction mixture may contain incidental low levels of total water that are in the ionic liquid, in the cellulose or lignocellulose, or otherwise enter the reaction vessel. Cellulose or lignocellulose itself can contain water dependent upon the source and physical form of the cellulose. Cellulose can, for example, contain 10-15% by weight water. Lignocellulosic materials subjected to pretreatment, for example dilute acid pretreatment, may contain water. Typically, such incidental water is present at levels of at most about 5 weight % of all reaction components. When incidental water levels are lower than about 5 weight % of all reaction components, water may optionally be added to the initial reaction mixture up to a level of about 5 weight % with respect to all reaction components. A portion of this initially added water may be added to facilitate acid addition. Any known amounts of water in the cellulose or added to the initial reaction mixture is considered in the determination of total water content, when water is added after the reaction is initiated. Initial water content is preferably sufficiently low to avoid any substantial cellulose precipitation. Cellulose precipitation can, for example, be detected visually by cloudiness in the ionic liquid. If the water content of the material to be hydrolyzed is over about 5% by weight, lignocellulosic materials or cellulose are optionally subjected to at least partial drying before hydrolysis to reduce water levels to about 5 weight % or less. Water-levels in material to be hydrolyzed can be determined by any method known in the art. Water levels in the material to be hydrolyzed should be sufficiently low to avoid precipitation, when the materials are added to and at least partially dissolved in ionic liquid.

[0035]The ionic liquid chloride salt dissolves cellulose and is believed to facilitate enhanced yield of glucose. Cellulose is introduced into the ionic liquid and vigorously stirred or mixed to aid dissolution. Optionally, the cellulose is stirred in the ionic liquid for at least an hour prior to adding acid and initiating the reaction. Enhanced glucose yield can be obtained if the cellulose is mixed with the ionic liquid for up to 3, up to 6 or up to 9 hours prior to initiation of reaction. This premixing of the ionic liquid with lignocellulose can be performed at ambient temperature or at a temperature above ambient up to 140 C, dependent upon the melting or softening point of the ionic liquid. The ionic liquid should be liquid or at least softened (so that it can be mixed). More specifically, the premixing can be performed at reaction temperature, specifically at a temperature between 70 and 140° C.

[0036]The ionic liquid chloride salt decrystallizes lignocellulose and at least partially dissolves cellulose therein. The ionic liquid is believed to facilitate enhanced yield of glucose. Lignocellulose is introduced into the ionic liquid and vigorously stirred or mixed to aid decrystalization or dissolution. Optionally, the lignocellulose is stirred in the ionic liquid for at least an hour prior to adding acid and initiating the reaction. Enhanced glucose yield can be obtained if the lignocellulose is mixed with the ionic liquid for up to 3, up to 6 or up to 9 hours prior to initiation of reaction. This premixing of the ionic liquid with lignocellulose can be performed at ambient temperature or at a temperature above ambient up to 140° C., dependent upon the melting or softening point of the ionic liquid. The ionic liquid should be liquid or at least softened (so that it can be mixed). More specifically, the premixing can be performed at reaction temperature, specifically at a temperature between 70 and 140° C.

Problems solved by technology

The challenge for chemists is to access these polymers and convert them into fuels and chemical building blocks.

Deriving sugars from this heterogeneous feedstock requires both physical and chemical disruption.

Nonetheless, the costs of both pretreatment and enzymes (estimated to be as much as one-third of the cost of ethanol production from cellulose, [12]) and low rates of hydrolysis are potential drawbacks to enzymatic hydrolysis.

Concentrated acid hydrolysis methods produce high sugar yields, use simple catalysts, and require only short reaction times. Despite these advantages, the hazards of handling concentrated acids and the complexities of recycling them have limited the adoption of this technology.

However, excessively high amounts of water in the reaction mixture may result in either reduced solubility of the cellulose in the ionic liquid, and / or reduced conversion of cellulose to water-soluble hydrolysis products.

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